1. Art Field
The present invention relates generally to a novel heat-resistant, low-dielectric polymeric material, and films, substrates, electronic parts and heat-resistant resin formed articles obtained by use of the same. Specifically, the present invention is concerned with a low-dielectric-constant polymeric material that has a low dielectric constant and a low dielectric loss tangent, is excellent in heat resistance in a high-temperature range and close contact with or adhesion to metals and metal foils as well, and is capable of injection molding, press molding, transfer molding and extrusion molding. More specifically, the present invention is directed to a substrate or the like that is prepared by thermal fusion and lamination of films obtainable from the low-dielectric-constant polymeric material itself.
2. Background Art
To meet recent sharp increases in the quantity of information communications, there are growing demands for size and weight reductions, and fast operation of communications equipment and, hence, low-dielectric electrical insulating materials capable of meeting such demands are now in urgent need. In particular, the frequencies of radio waves used for hand-portable mobile communications such as earphones and digital portable phones, and satellite communications are in high-frequency bands covering from the MHz to GHz bands. Size reductions, and high-density packing of housings, substrates and elements are attempted on account of the rapid progress of communications equipment used as these communications means. For achieving size and weight reductions of communications equipment used in the high-frequency band region covering from the MHz to GHz bands, it is now required to develop an electrical insulating material with excellent high-frequency transmission characteristics combined with suitable low dielectric characteristics. In other words, a device circuit undergoes energy losses in the transmission process, which are called dielectric losses. The energy losses are not preferable because they are consumed as thermal energy in the device circuit, and discharged in the form of heat. In a low-frequency region the energy losses occur due to a dipole field change caused by dielectric polarization, and in a high-frequency region they occur due to ionic polarization and electronic polarization. The ratio between the energy consumed in a dielectric material and the energy built up in the dielectric material per cycle of an alternating field is referred to as a dielectric loss tangent, represented by tan xcex4. A dielectric loss is proportional to the product of a relative dielectric constant ∈ and the dielectric loss tangent of material. Consequently, tan xcex4 increases with increasing frequency in the high-frequency region. In addition, the quantity of heat generated per unit area increases due to the high-density packing of electronic elements. To reduce the dielectric loss of a dielectric material as much as possible, therefore, it is required to use a material having a small value for tan xcex4. By use of a low-dielectric polymeric material having a reduced dielectric loss, the dielectric loss and the generation of heat due to electrical resistance are reduced so that the risk of signal malfunctions can be reduced. Materials having reduced transmission losses (energy losses) are thus strongly desired in the field of high-frequency communications. For materials electrically characterized by electrical insulation and a low-dielectric constant, it has been proposed so far in the art to use a diversity of materials such as thermoplastic resins, e.g., polyolefin, vinyl chloride resin and fluorine base resin, and thermosetting resins, e.g., unsaturated polyester resin, polyimide resin, epoxy resin, vinyltriazine resin (BT resin), crosslinkable polyphenylene oxide, and curable polyphenylene ether.
When materials having a low-dielectric constant are used as an electronic part (element) material, however, polyolefins such as polyethylene and polypropylene, like those set forth in JP-B 52-31272, have a grave disadvantage that their heat resistance is low although they have excellent insulation resistance as electrical properties. This is because they have a covalent bond such as a Cxe2x80x94C bond, and are free of a large polar group. For this reason, their electrical properties (dielectric loss, dielectric constant, etc.) become worse when they are used at high temperatures. Thus, such polyolefins are not preferable for use as an insulating film (layer) for capacitors, etc. The polyethylene and polypropylene, once they have been formed into film, are coated and bonded onto a conductive material using an adhesive agent. However, this method does not only involve a complicated process but also offers some problems in view of coating, for instance, because it is very difficult to make the thickness of the film thin.
The vinyl chloride resin has high insulation resistance and excellent chemical resistance and fire retardance, but it has the demerits of lacking heat resistance as in the case of polyolefins, and having large dielectric losses as well.
Polymers containing a fluorine atom in their molecular chains, like vinylidene fluoride resin, trifluoroethylene resin, and perfluoroethylene resin, are excellent in terms of electrical properties (low dielectric constant, low-dielectric loss), heat resistance and chemical stability. However, one difficulty with such polymers is that, unlike thermoplastic resins, they cannot be heat-treated into formed articles or films due to their poor formability, and their poor ability to form coatings. Another disadvantage is that some added cost is needed for forming the polymers into devices. Yet another disadvantage is that the field to which the polymers are applicable is limited due to their low transparency. Such low-dielectric polymeric materials for general purpose use as mentioned above are all insufficient in terms of heat resistance because their allowable maximum temperature is below 130xc2x0 C. and, hence, they are classified as an insulating material for electrical equipment into heat resistance class B or lower according to JIS-C4003.
On the other hand, the thermosetting resins such as epoxy resin, polyphenylene ether (PPE), unsaturated polyester resin, and phenolic resin are mentioned for resins having relatively good heat resistance. As disclosed in JP-A 6-192392, the epoxy resin conforms to performance requirements regarding insulation resistance, dielectric breakdown strength, and heat-resistant temperature. However, no satisfactory properties are obtained because of a relatively high dielectric constant of 3 or greater. The epoxy resin has another demerit of being poor in the ability to form thin films. In addition, a curable modified PPO resin composition is known, which composition is obtained by blending polyphenylene oxide resin (PPO) with polyfunctional cyanic acid ester resins and other resins, and adding a radical polymerization initiator to the blend for preliminary reactions. However, this resin, too, fail to reduce the dielectric constant to a satisfactory level.
With a view to improving the epoxy resin having poor heat resistance, combinations of the epoxy resin with, for instance, phenol-novolak resin, and vinyltriazine resin have been under investigation. However, a grave problem with these combinations is some significant drop of the dynamic properties of the resulting films.
For the purposes of solving the above problems while the electrical properties are maintained, and specifically introducing improvements in the processability on heating, and close contact with or adhesion to copper or other metal conductors (layers), proposals have been put forward for copolymers of branched cyclo-ring amorphous fluoropolymer, and perfluoroethylene monomer with other monomers. However, although these copolymers may satisfy electrical properties such as dielectric constant, and dielectric loss tangent, yet their heat resistance remains worse under the influence of a methylene chain present in the high-molecular main chain. Never until now, thus, is there obtained any resin that can come in close contact with device substrates.
Among performance requirements for a low-dielectric-constant material excellent in dielectric properties and insulation resistance, there is heat resistance. That is, such a material can stand up well to a 120-second heating at a temperature of at least 260xc2x0 C. because a soldering step is always incorporated in a device fabrication process. Stated otherwise, the material should also be excellent in heat resistance, chemical stability such as alkali resistance, humidity resistance, and mechanical properties. Thus, the range of high-molecular materials capable of meeting such requirements is further limited. For instance, polyimide, polyether sulfone, polyphenylene sulfide, polysulfone, thermosetting polyphenylene ether (PPE), and polyethylene terephthalate are only known in the art. While these high-molecular materials are capable of forming thin films and coming in close contact with substrates, it is found that they are somewhat awkward. In a process of fabricating an insulating element film by, e.g., spin coating, the aforesaid high-molecular material is dissolved in an organic solvent to form a dilute solution. Then, the solution is spin coated, followed by evaporation of the solvent, yielding an insulating film. Solvents such as dimethylacetamide, and N-methylpyrrolidone that are good solvents for polyimide, and polysulfone are likely to remain partially in the insulating film because they are a polar yet high-boiling solvent and so have a low evaporation speed. It is also difficult to place the surface smoothness and consistency of thin films under control. Epoxy-modified polyphenylene ether resin or polyphenylene ether resin, too, is poor in workability and adhesion and, hence, reliability. In addition, much skill is required to form a uniform yet smooth film from a polymer solution because the polymer solution has a relatively high viscosity.
One object of the present invention is to provide a low-dielectric-constant polymeric material which has heat resistance, and is excellent in close contact with or adhesion to a metal conductor layer, capable of forming a thin film, low in terms of dielectric constant and dielectric loss, and excellent in insulating properties, and weather resistance and processability as well.
Another object of the invention is to provide a film which is obtained from the low-dielectric-constant polymeric material itself, and which has a low-dielectric constant, and is improved in terms of insulating properties, heat resistance, weather resistance, and processabilities such as formability. Yet another object of the invention is to provide a substrate which is obtained by lamination of two or more such films, and which has a low-dielectric constant and is improved in terms of insulating properties, heat resistance, weather resistance and processabilities such as formability. Still yet another object of the invention is to provide an electronic part which is obtained from the low-dielectric-constant polymeric material, and which is suitable for use in a high-frequency region. A further object of the invention is to provide a heat-resistant resin formed article improved in terms of heat resistance and formability.
Such objects are achieved by the inventions defined below as (1) to (14).
(1) A heat-resistant, low-dielectric polymeric material that is a resin composition comprising one or two or more resins having a weight-average absolute molecular weight of at least 1,000, wherein the sum of carbon atoms and hydrogen atoms in said composition is at least 99%, and some or all resin molecules have a chemical bond therebetween.
(2) The heat-resistant, low-dielectric polymeric material according to (1), wherein said chemical bond is at least one bond selected from crosslinking, block polymerization, and graft polymerization.
(3) The heat-resistant, low-dielectric polymeric material according to (1), wherein said resin composition is a copolymer in which a non-polar xcex1-olefin base polymer segment and/or a non-polar conjugated diene base polymer segment are chemically combined with a vinyl aromatic polymer segment, and which shows a multi-phase structure wherein a dispersion phase formed by one segment is finely dispersed in a continuous phase formed by another segment.
(4) The heat-resistant, low-dielectric polymeric material according to (3), which is a copolymer with said xcex1-olefin base polymer segment chemically combined with said vinyl aromatic polymer segment.
(5) The heat-resistant, low-dielectric polymeric material according to (3), wherein said vinyl aromatic polymer segment is a vinyl aromatic copolymer segment containing a monomer of divinylbenzene.
(6) The heat-resistant, low-dielectric polymeric material according to (4), which is a copolymer chemically bonded by graft polymerization.
(7) A heat-resistant, low-dielectric polymeric material, wherein a non-polar xcex1-olefin base polymer containing a monomer of 4-methylpentene-1 is added to the resin composition according to (1).
(8) The heat-resistant, low-dielectric polymeric material according to (1), which is used in a high-frequency band of at least 1 MHz.
(9) A film of at least 50 xcexcm in thickness, which is obtained using the heat-resistant, low-dielectric polymeric material according to (1).
(10) A substrate obtained by lamination of films, each according to (9).
(11) The film according to (9), which is used in a high-frequency band of at least 1 MHz.
(12) The substrate according to (10), which is used in a high-frequency band of at least 1 MHz.
(13) An electronic part, which is obtained using the heat-resistant, low-dielectric polymeric material according to (1) and used in a high-frequency band of at least 1 MHz.
(14) A heat-resistant resin article obtained by forming the heat-resistant, low-dielectric polymeric material according to (1) into a given shape.